1. Field of the Invention
The present invention relates to an inspection apparatus, an inspection method, an inspection system, and a storage medium. More particularly, the present invention relates to an inspection apparatus, an inspection method, an inspection system, and a storage medium useful for inspecting a printed product having an image printed thereon.
2. Description of the Related Art
Conventionally, there have been a print image inspection system which determines (inspects) whether a printed product has a defect. This system can be used for a printing and bookbinding system such as a Print on Demand (POD) apparatus. As a method for inspecting a printed product, there is a method in which an image input in a printing apparatus (also referred to as a reference image) is compared with an image of a printed product output from the printing apparatus and read by a reading apparatus such as a scanner (also referred to as a print image).
According to a method discussed in Japanese Patent Application Laid-Open No. 2007-085870, if there is misregistration of the images, a comparison inspection of the images is performed after the positional alignment of the images are performed.
Further, Japanese Patent Application Laid-Open No. 2008-197917 discusses a positional alignment method of a reference image and a print image by extracting feature points, such as an edge, from both the reference image and the print image, and performing geometric transformation of the images after detecting a correspondence relation of the feature points extracted from the images.
As discussed in Japanese Patent Application Laid-Open No. 2007-085870, it is necessary to perform the positional alignment of the images in accurately comparing the reference image and the print image. The positional alignment method discussed in Japanese Patent Application Laid-Open No. 2008-197917 performs the positional alignment of the images based on the feature points which are extracted from edge information of a line or a character in the image.
However, the feature points cannot be extracted or, even if they are extracted, the number of the extracted feature points may be extremely small depending on the image that is processed. In such a case, even if the positional alignment processing is performed for the reference image and the print image, the accuracy of the positional alignment may be low. For example, if the reference image is a gradation image, an edge, from which the feature points are extracted, may not be obtained. Further, for example, if the reference image is a natural picture, the number of the edges which can be extracted may be extremely small. In such a case, the number of the feature points which are extracted may not be sufficient for performing high-precision positional alignment.
If comparison processing with the positional alignment processing being required is performed with respect to a reference image and a print image which are not suitable for high precision positional alignment, a good printed product maybe determined as defective due to low positional alignment accuracy.